Topic 4 Flashcards
alkenes are which kind of hydrocarbons
unsaturated
what is the general formula for alkenes
CnH2n
what prohibits rotation in alkenes
the pi bond
it locks the 2 carbon atoms into position
what is the shape around the carbon atoms in the double bond and why
120 degree bond angle
repel each other equally
in the same plane
trigonal planar
3 regions of electron density
what is stereoisomerism
same structural formula but a different arrangement of atoms in space
what are the 2 types of stereoisomerism
E/Z isomerism
Optical isomerism
when is cis/trans isomerism applicable
when molecules has C=C double bonds
Each carbon atom in double bond is attached to 2 different groups
what is the cis isomer
hydrogen atoms on each carbon are on the same side
what is the trans isomer
hydrogen atoms are diagonally opposite each other
what are the Cahn-Ingold Prelog rules for deciding E/Z isomerism
higher atomic number = higher priority
groups of higher priority on the same side of the double bond of the Z isomer
describe hydrogenation of alkenes
an alkene is mixed with hydrogen and passed over a nickel catalyst at 423K forming an alkane
describe halogenation of alkenes
Rapid addition reaction between an alkene and Cl/Br at room temperature to form a halogenalkane
how do you test for alkenes
orange bromine water turns clear
describe hydration of alkenes
an alkene is reacted with steam in the presence of a phosphoric acid catalyst, forming an alcohol
2 products can be formed
what is the mechanism for addition reaction
electrophilic addition
outline an electrophilic addition reaction between an alkene and hydrogen bromide
H-Br is a polar molecule
electron pair in a pi bond is attracted to it
double bond breaks
bonds forms H and C atoms
H-Br bond breaks by heterolytic fission
bromide ion and carbocation formed
Br- reacts with carbocation
how does electrophilic addition take place with molecules with molecules that are non-polar
when the molecule approaches the pi bond, the electrons in the bond are repelled and this induces polarity
what is the Markownikoff’s rule
In electrophilic addition, when the carbocation is formed, it can be primary, secondary, tertiary.
Tertiary is the most stable so is the most likely product
what is carbocation
positively charged molecule of carbon
why is tertiary carbocation the most stable
connecting alkyl groups donate and push electrons towards the positive charge of the carbocation
therefore more alkyl groups = a more stable ions
what is the name of the reaction for a polymer’s formation from alkenes
addition polymer
how is the monomer unit displayed
displayed formula with an (n) before it to signify many units
how is the repeat unit of the polymer are displayed
displayed formula, in square brackets, an (n) is placed after to signify a large number of repeats
what are the conditions for a polymerisation reaction
high temperature and pressure
what are the uses of polypropene
Toys, packing crates, guttering, rope fibre
what are the uses of polyphenylethene - polystyrene
packaging materials
food trays + cups
what are the uses of polytetra fluroethene
coating for non-stick pans
permeable membrane for clothing
cable insulation
downside of current disposal of waste of polymers?
very unreactive
non-biodegradable with serious environmental effects
what are the benefits of recycling polymers
reduces environmental impacts by conserving fossil fuels and decreasing waste
how is a double bond formed
3 sigma bonds formed
1 electron left in a p-orbital
a pi bond forms from the sideways overlap of 2 p-orbitals
what is an elimination reaction
the removal of a small molecule from a larger one
what is the functional group and suffix for
an alkene
alcohols
aldehyde
ketones
carboxylic acids
c=c -ene
OH -ol
-CHO -al
C(CO)C -one
COOH -oic acid
functional group and prefix for haloalkane
-Cl/-Br/-I
Chloro-
Bromo-
Iodo-
what is the difference between a saturated and unsaturated hydrocarbon
saturated = only single bonds
unsaturated = mutiple bonds
what is a homologous series
family of compounds with similar chemical properties differing by the addition of a group
what is a functional group
part of the organic molecule that is responsible for the molecules chemical properties
what is an aliphatic hydrocarbon
carbon atoms are joined to each other in a straight chain
what is an alicyclic hydrocarbon
carbon atoms are joined to each other in a ring (cyclic) structure
what is an aromatic hydrocarbon
some/all carbon atoms are found in a benzene rings
what is the difference between alkanes, alkenes and alkynes
ane - single C-C bonds
ene - one+ C=C double bond
yne - 1+ C-C triple bond
what is a general formula
simplest algebraic formula for any member of a homologous series
what is displayed formula
shows relative positioning of all of the atoms in a molecule + the bonds
what is the structural formula
shows which groups are bonded together
CH3CH2CH3
hwo is skeletal formula formed
remove all of the carbon and hydrogen labels from the carbon chain
remove any bonds to hydrogen atoms
how does skeletal formula work
one line = a single bond
intersection of 2 lines = a carbon atom
end of a line = -CH3 group
what is a structural isomer
compounds with the same molecular formula but different structural formula
what is homolytic fission and what is formed after
when a covalent bond breaks, each of the bonded atoms takes 1 electron from the shared pair
2 atoms with an unpaired electron - radicals
what is heterolytic fission and what is formed after
whena covalent bond breaks, 1 bonded atom takes both of the electrons fro the shared pair
a positive ion ad a negative ion
what are curly arrows used to show
movement of electron pairs when bonds are broken or made
what is an addition reaction
2 reactants form 1 product after being joined together
what is a substitution reaction
an atom/group of atoms is replaced by a different atoms/group ofatoms
what is the main use of alkanes
fuel
what is the general formula of alkanes
CnH2n+2
what kind of covalent bonds are formed in alkanes
sigma bonds
what is a sigma bond
the overlap of 2 orbitals
how are alkanes separated
fractional distillation
how does chain length affect bp and why
longer chain length raises boiling point as there is a greater surface area of contact which means stronger London forces which require more energy to overcome
what is the effect of branching on bp and why
lowers boiling point as there is less surface area of contact which means weaker London forces which require less energy to overcome
why are alkanes fairly unreactive
C-C, C-H sigma bonds are strong
C-C bonds are non polar
Similar electronegativity of carbon and hydrogen
what is complete combustion and what are the products
alkanes burn completely to produce CO2 and H2O
what are the 2 products from incomplete combustion of alkanes
carbon monoxide and water
name the mechanism for bromination of alkanes
free radical substitution
what are the 3 stages of free radical substitution
initiation
propagation
substitution
describe initiation of free radical substitution
covalent bond in a bromine molecule is broken by homolytic fission
energy is provided by UV radiation
Br-Br -> *Br + *Br
describe propagation stage of free radical substitution
CH4 + Br* –> CH3 + HBR
CH3 + Br2 –> CH3BR + Br*
describe termination stage of free radical substitution
2 radicals collide forming a molecule with all electrons paired
1. Br* + Br* –> Br2
2. *CH3 + *CH3 –> C2H6
3. CH3 + Br –> CH3Br
what can occur after a radical substitution reaction
further substitution
